Allylic alcohols transition metal peroxides

Lewis acids such as SnCl4 also catalyze the reaction, in which case the species that adds to the alkenes is H2C —O— SnC. Montmorillonite KIO clay containing zinc(IV) has been used to promote the reaction. The reaction can also be catalyzed by peroxides, in which case the mechanism is probably a free-radical one. Other transition metal complexes can be used to form allylic alcohols. A typical example is. ... 

Metals that are capable of 2e redox changes, typically main group elements and 4d and 5d transition metals, can give heterolysis of a peroxide to form a diamagnetic oxidant that may avoid the radical pathways seen in the case of equation (14-15). O atom transfer to the substrate is possible in this way. Sharpless epoxidation provides an excellent example. In this case rBuOOH is the primary oxidant, Ti(i-OPr)4 is the catalyst precursor and a tartrate ester is the ligand that induces a high ee in the epoxy alcohol formed from an allylic alcohol. This reaction has been successfiiUy developed on an industrial scale. 

AE reactions of simple olefins. The Sharpless AE reaction has been supplemented by other approaches to asymmetric epoxide synthesis the most evident goal being to obviate the need for an allylic alcohol. Attempts to carry out asymmetric epoxidation reactions on simple olefins have utilized transition-metal-containing catalysts such as porphyrins as well as stoichiometric chiral reagents (peroxides, dioxiranes, and oxaziridines). These approaches have been summarized [19]. 

When the previously cited transition structure 193 is applied to the asymmetric epoxidation of allylic alcohols, it must be modified to include binding of the peroxide, the allylic alcohol, and also the chiral tartrate. The metal in the new model is titanium rather than vanadium, and tetraisopropoxy titanium was found to react with 2 equivalents of diethyl tartrate to form a species such as 212, where OR = 0/-Pr and CO2R = CO2Et.3i7.3i8 The tartrate can bind to titanium from either the bottom or the top face.3i8 The nature of the... 

Sharpless asymmetric epoxidation (SAE) is the epoxidation of allylic alcohols into asymmetric epoxides in high chiral purity (high enantioselectiv-ity). Transition metal catalyst Ti(OPr ) with chiral additive, diethyl tartarate (DET), generates chiral catalyst (Scheme 9.40) which is responsible for the enantioselective outcome, while, tert-butyl hydroperoxide (TBHP) serves as an oxidant. Although, this eatalytic system holds disadvantage of low turnover number (TON) with potential safety coneems for using concentrated solutions of peroxides, the reaction has nevertheless been extensively used in pharmaceutical industry [76]. 

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